Field of the Invention
This invention relates to a molding sand for three dimensional laminate molding (e.g., 3D printing, additive manufacturing) for use in an organic self-hardening mold for molding, and particularly to a molding sand for a sand mold with no veining defect occurring upon molding.
Related Art
Currently, molded products with various shapes, sizes and materials are used in various fields.
Also, in recent years, as products difficult to cast, products requiring a complicated mold, i.e. sand mold have been increasing. Therefore, a sand mold (mold) by an organic binder with characteristics that after molding, a molding sand is easily removed to easily produce, also the strength is high, deformation is less, and the like has actively been used.
On the other hand, as a raw material of a cylinder head for a large diesel engine which is required to have higher strength as compared to small one for an automobile, cast iron, which has a high melting point and is difficult to be molded, is adopted.
Here, as a method for producing a sand mold into which the above cast iron is cast, there is a three dimensional laminate molding method, i.e. RP (rapid prototyping) molding method, and this method is a technique for producing a sand mold directly from 3DCAD data (e.g. Patent Document 1). This RP molding method has advantages in that a sand mold with a complicated shape can easily be produced and the dimension accuracy is good.
Moreover, the RP molding method using a mold by an organic binder is classified into a two liquid mixed self-hardening type of printing a resin to a sand having a hardening agent as a catalyst for hardening a resin mixed, and a thermohardening type of illuminating laser to a sand having been coated with resin in advance (RCS: resin coated sand) to harden.
Here, the thermohardening type of three dimensional laminate molding is, since the resin used is excellent in heat resistance, possible to be applied to many materials from aluminum alloy to be cast into at a low temperature to cast iron and cast steel to be cast into at a high temperature. Therefore, for high melting point metal such as cast iron, the thermohardening type has conventionally been used.